bn_sqr.c revision 340704 
1/* crypto/bn/bn_sqr.c */
2/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
3 * All rights reserved.
4 *
5 * This package is an SSL implementation written
6 * by Eric Young (eay@cryptsoft.com).
7 * The implementation was written so as to conform with Netscapes SSL.
8 *
9 * This library is free for commercial and non-commercial use as long as
10 * the following conditions are aheared to.  The following conditions
11 * apply to all code found in this distribution, be it the RC4, RSA,
12 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
13 * included with this distribution is covered by the same copyright terms
14 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
15 *
16 * Copyright remains Eric Young's, and as such any Copyright notices in
17 * the code are not to be removed.
18 * If this package is used in a product, Eric Young should be given attribution
19 * as the author of the parts of the library used.
20 * This can be in the form of a textual message at program startup or
21 * in documentation (online or textual) provided with the package.
22 *
23 * Redistribution and use in source and binary forms, with or without
24 * modification, are permitted provided that the following conditions
25 * are met:
26 * 1. Redistributions of source code must retain the copyright
27 *    notice, this list of conditions and the following disclaimer.
28 * 2. Redistributions in binary form must reproduce the above copyright
29 *    notice, this list of conditions and the following disclaimer in the
30 *    documentation and/or other materials provided with the distribution.
31 * 3. All advertising materials mentioning features or use of this software
32 *    must display the following acknowledgement:
33 *    "This product includes cryptographic software written by
34 *     Eric Young (eay@cryptsoft.com)"
35 *    The word 'cryptographic' can be left out if the rouines from the library
36 *    being used are not cryptographic related :-).
37 * 4. If you include any Windows specific code (or a derivative thereof) from
38 *    the apps directory (application code) you must include an acknowledgement:
39 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
40 *
41 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
42 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
43 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
44 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
45 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
46 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
47 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
48 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
49 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
50 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
51 * SUCH DAMAGE.
52 *
53 * The licence and distribution terms for any publically available version or
54 * derivative of this code cannot be changed.  i.e. this code cannot simply be
55 * copied and put under another distribution licence
56 * [including the GNU Public Licence.]
57 */
58
59#include <stdio.h>
60#include "cryptlib.h"
61#include "bn_lcl.h"
62
63/* r must not be a */
64/*
65 * I've just gone over this and it is now %20 faster on x86 - eay - 27 Jun 96
66 */
67int BN_sqr(BIGNUM *r, const BIGNUM *a, BN_CTX *ctx)
68{
69    int ret = bn_sqr_fixed_top(r, a, ctx);
70
71    bn_correct_top(r);
72    bn_check_top(r);
73
74    return ret;
75}
76
77int bn_sqr_fixed_top(BIGNUM *r, const BIGNUM *a, BN_CTX *ctx)
78{
79    int max, al;
80    int ret = 0;
81    BIGNUM *tmp, *rr;
82
83#ifdef BN_COUNT
84    fprintf(stderr, "BN_sqr %d * %d\n", a->top, a->top);
85#endif
86    bn_check_top(a);
87
88    al = a->top;
89    if (al <= 0) {
90        r->top = 0;
91        r->neg = 0;
92        return 1;
93    }
94
95    BN_CTX_start(ctx);
96    rr = (a != r) ? r : BN_CTX_get(ctx);
97    tmp = BN_CTX_get(ctx);
98    if (!rr || !tmp)
99        goto err;
100
101    max = 2 * al;               /* Non-zero (from above) */
102    if (bn_wexpand(rr, max) == NULL)
103        goto err;
104
105    if (al == 4) {
106#ifndef BN_SQR_COMBA
107        BN_ULONG t[8];
108        bn_sqr_normal(rr->d, a->d, 4, t);
109#else
110        bn_sqr_comba4(rr->d, a->d);
111#endif
112    } else if (al == 8) {
113#ifndef BN_SQR_COMBA
114        BN_ULONG t[16];
115        bn_sqr_normal(rr->d, a->d, 8, t);
116#else
117        bn_sqr_comba8(rr->d, a->d);
118#endif
119    } else {
120#if defined(BN_RECURSION)
121        if (al < BN_SQR_RECURSIVE_SIZE_NORMAL) {
122            BN_ULONG t[BN_SQR_RECURSIVE_SIZE_NORMAL * 2];
123            bn_sqr_normal(rr->d, a->d, al, t);
124        } else {
125            int j, k;
126
127            j = BN_num_bits_word((BN_ULONG)al);
128            j = 1 << (j - 1);
129            k = j + j;
130            if (al == j) {
131                if (bn_wexpand(tmp, k * 2) == NULL)
132                    goto err;
133                bn_sqr_recursive(rr->d, a->d, al, tmp->d);
134            } else {
135                if (bn_wexpand(tmp, max) == NULL)
136                    goto err;
137                bn_sqr_normal(rr->d, a->d, al, tmp->d);
138            }
139        }
140#else
141        if (bn_wexpand(tmp, max) == NULL)
142            goto err;
143        bn_sqr_normal(rr->d, a->d, al, tmp->d);
144#endif
145    }
146
147    rr->neg = 0;
148    rr->top = max;
149    rr->flags |= BN_FLG_FIXED_TOP;
150    if (r != rr && BN_copy(r, rr) == NULL)
151        goto err;
152
153    ret = 1;
154 err:
155    bn_check_top(rr);
156    bn_check_top(tmp);
157    BN_CTX_end(ctx);
158    return (ret);
159}
160
161/* tmp must have 2*n words */
162void bn_sqr_normal(BN_ULONG *r, const BN_ULONG *a, int n, BN_ULONG *tmp)
163{
164    int i, j, max;
165    const BN_ULONG *ap;
166    BN_ULONG *rp;
167
168    max = n * 2;
169    ap = a;
170    rp = r;
171    rp[0] = rp[max - 1] = 0;
172    rp++;
173    j = n;
174
175    if (--j > 0) {
176        ap++;
177        rp[j] = bn_mul_words(rp, ap, j, ap[-1]);
178        rp += 2;
179    }
180
181    for (i = n - 2; i > 0; i--) {
182        j--;
183        ap++;
184        rp[j] = bn_mul_add_words(rp, ap, j, ap[-1]);
185        rp += 2;
186    }
187
188    bn_add_words(r, r, r, max);
189
190    /* There will not be a carry */
191
192    bn_sqr_words(tmp, a, n);
193
194    bn_add_words(r, r, tmp, max);
195}
196
197#ifdef BN_RECURSION
198/*-
199 * r is 2*n words in size,
200 * a and b are both n words in size.    (There's not actually a 'b' here ...)
201 * n must be a power of 2.
202 * We multiply and return the result.
203 * t must be 2*n words in size
204 * We calculate
205 * a[0]*b[0]
206 * a[0]*b[0]+a[1]*b[1]+(a[0]-a[1])*(b[1]-b[0])
207 * a[1]*b[1]
208 */
209void bn_sqr_recursive(BN_ULONG *r, const BN_ULONG *a, int n2, BN_ULONG *t)
210{
211    int n = n2 / 2;
212    int zero, c1;
213    BN_ULONG ln, lo, *p;
214
215# ifdef BN_COUNT
216    fprintf(stderr, " bn_sqr_recursive %d * %d\n", n2, n2);
217# endif
218    if (n2 == 4) {
219# ifndef BN_SQR_COMBA
220        bn_sqr_normal(r, a, 4, t);
221# else
222        bn_sqr_comba4(r, a);
223# endif
224        return;
225    } else if (n2 == 8) {
226# ifndef BN_SQR_COMBA
227        bn_sqr_normal(r, a, 8, t);
228# else
229        bn_sqr_comba8(r, a);
230# endif
231        return;
232    }
233    if (n2 < BN_SQR_RECURSIVE_SIZE_NORMAL) {
234        bn_sqr_normal(r, a, n2, t);
235        return;
236    }
237    /* r=(a[0]-a[1])*(a[1]-a[0]) */
238    c1 = bn_cmp_words(a, &(a[n]), n);
239    zero = 0;
240    if (c1 > 0)
241        bn_sub_words(t, a, &(a[n]), n);
242    else if (c1 < 0)
243        bn_sub_words(t, &(a[n]), a, n);
244    else
245        zero = 1;
246
247    /* The result will always be negative unless it is zero */
248    p = &(t[n2 * 2]);
249
250    if (!zero)
251        bn_sqr_recursive(&(t[n2]), t, n, p);
252    else
253        memset(&(t[n2]), 0, n2 * sizeof(BN_ULONG));
254    bn_sqr_recursive(r, a, n, p);
255    bn_sqr_recursive(&(r[n2]), &(a[n]), n, p);
256
257    /*-
258     * t[32] holds (a[0]-a[1])*(a[1]-a[0]), it is negative or zero
259     * r[10] holds (a[0]*b[0])
260     * r[32] holds (b[1]*b[1])
261     */
262
263    c1 = (int)(bn_add_words(t, r, &(r[n2]), n2));
264
265    /* t[32] is negative */
266    c1 -= (int)(bn_sub_words(&(t[n2]), t, &(t[n2]), n2));
267
268    /*-
269     * t[32] holds (a[0]-a[1])*(a[1]-a[0])+(a[0]*a[0])+(a[1]*a[1])
270     * r[10] holds (a[0]*a[0])
271     * r[32] holds (a[1]*a[1])
272     * c1 holds the carry bits
273     */
274    c1 += (int)(bn_add_words(&(r[n]), &(r[n]), &(t[n2]), n2));
275    if (c1) {
276        p = &(r[n + n2]);
277        lo = *p;
278        ln = (lo + c1) & BN_MASK2;
279        *p = ln;
280
281        /*
282         * The overflow will stop before we over write words we should not
283         * overwrite
284         */
285        if (ln < (BN_ULONG)c1) {
286            do {
287                p++;
288                lo = *p;
289                ln = (lo + 1) & BN_MASK2;
290                *p = ln;
291            } while (ln == 0);
292        }
293    }
294}
295#endif
296